Dynamic control of transcutaneous electrical nerve stimulation therapy using continuous sleep detection

ABSTRACT

Apparatus for providing transcutaneous electrical nerve stimulation (TENS) therapy to a user, said apparatus comprising: a housing; an application unit for providing mechanical coupling between the housing and the user&#39;s body; a stimulation unit for electrically stimulating at least one nerve of the user; a sensing unit for (i) sensing the user&#39;s body movement and body orientation to determine whether the user is in an “out-of-bed” state or a “rest-in-bed” state, and (ii) analyzing the sleep characteristics of the user during the “rest-in-bed” state; and a feedback unit for at least one of (i) providing the user with feedback in response to the analysis of the sleep characteristics of the user, and (ii) modifying the electrical stimulation provided to the user by the stimulation unit in response to the analysis of the sleep characteristics of the user; wherein the sleep characteristics comprise a likelihood measure of the user&#39;s sleep quality.

REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

This patent application:

(1) is a continuation-in-part of pending prior U.S. patent applicationSer. No. 15/602,611, filed May 23, 2017 by NeuroMetrix, Inc. and Shai N.Gozani et al. for APPARATUS AND METHOD FOR RELIEVING PAIN USINGTRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (Attorney's Docket No.NEURO-5960 CON 2), which patent application:

-   -   (A) is a continuation of prior U.S. patent application Ser. No.        14/610,757, filed Jan. 30, 2015 by NeuroMetrix, Inc. and Shai N.        Gozani et al. for APPARATUS AND METHOD FOR RELIEVING PAIN USING        TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (Attorney's Docket        No. NEURO-5960 CON), which patent application in turn:        -   (i) is a continuation of prior U.S. patent application Ser.            No. 13/678,221, filed Nov. 15, 2012 by NeuroMetrix, Inc. and            Shai N. Gozani et al. for APPARATUS AND METHOD FOR RELIEVING            PAIN USING TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION            (Attorney's Docket No. NEURO-5960), which in turn claims            benefit of:            -   (a) prior U.S. Provisional Patent Application Ser. No.                61/560,029, filed Nov. 15, 2011 by Shai N. Gozani for                SENSUS OPERATING MODEL (Attorney's Docket No. NEURO-59                PROV); and            -   (b) prior U.S. Provisional Patent Application Ser. No.                61/657,382, filed Jun. 8, 2012 by Shai N. Gozani et al.                for APPARATUS AND METHOD FOR RELIEVING PAIN USING                TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (Attorney's                Docket No. NEURO-60 PROV);

(2) is a continuation-in-part of pending prior U.S. patent applicationSer. No. 14/980,041, filed Dec. 28, 2015 by NeuroMetrix, Inc. and ThomasFerree et al. for TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITHAUTOMATIC DETECTION OF LEG ORIENTATION AND LEG MOTION FOR ENHANCED SLEEPANALYSIS, INCLUDING ENHANCED TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION(TENS) USING THE SAME (Attorney's Docket No. NEURO-77), which patentapplication:

-   -   (A) is a continuation-in-part of prior U.S. patent application        Ser. No. 14/794,588, filed Jul. 8, 2015 by NeuroMetrix, Inc. and        Xuan Kong et al. for MEASURING THE “ON-SKIN” TIME OF A        TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR (TENS) DEVICE IN        ORDER TO MINIMIZE SKIN IRRITATION DUE TO EXCESSIVE UNINTERRUPTED        WEARING OF THE SAME (Attorney's Docket No. NEURO-73), which        patent application:        -   (i) is a continuation-in-part of prior U.S. patent            application Ser. No. 14/610,757, filed Jan. 30, 2015 by            NeuroMetrix, Inc. and Shai N. Gozani et al. for APPARATUS            AND METHOD FOR RELIEVING PAIN USING TRANSCUTANEOUS            ELECTRICAL NERVE STIMULATION (Attorney's Docket No.            NEURO-5960 CON), which patent application:            -   (a) is a continuation of prior U.S. patent application                Ser. No. 13/678,221, filed Nov. 15, 2012 by NeuroMetrix,                Inc. and Shai N. Gozani et al. for APPARATUS AND METHOD                FOR RELIEVING PAIN USING TRANSCUTANEOUS ELECTRICAL NERVE                STIMULATION (Attorney's Docket No. NEURO-5960), which                patent application claims benefit of:                -   (1) prior U.S. Provisional Patent Application Ser.                    No. 61/560,029, filed Nov. 15, 2011 by Shai N.                    Gozani for SENSUS OPERATING MODEL (Attorney's Docket                    No. NEURO-59 PROV); and                -   (2) prior U.S. Provisional Patent Application Ser.                    No. 61/657,382, filed Jun. 8, 2012 by Shai N. Gozani                    et al. for APPARATUS AND METHOD FOR RELIEVING PAIN                    USING TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION                    (Attorney's Docket No. NEURO-60 PROV);        -   (ii) is a continuation-in-part of pending prior U.S. patent            application Ser. No. 14/269,887, filed May 5, 2014 by            NeuroMetrix, Inc. and Thomas Ferree et al. for            TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH USER GESTURE            DETECTOR AND ELECTRODE-SKIN CONTACT DETECTOR, WITH TRANSIENT            MOTION DETECTOR FOR INCREASING THE ACCURACY OF THE SAME            (Attorney's Docket No. NEURO-6667), which patent            application:            -   (a) is a continuation-in-part of prior U.S. patent                application Ser. No. 14/230,648, filed Mar. 31, 2014 by                Neurometrix, Inc. and Shai Gozani et al. for DETECTING                CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKIN                IMPEDANCE (Attorney's Docket No. NEURO-64), which claims                benefit of:                -   (1) prior U.S. Provisional Patent Application Ser.                    No. 61/806,481, filed Mar. 29, 2013 by NeuroMetrix,                    Inc. and Shai Gozani for DETECTING ELECTRODE PEELING                    BY RELATIVE CHANGES IN SKIN-ELECTRODE IMPEDANCE                    (Attorney's Docket No. NEURO-64 PROV);            -   (b) is a continuation-in-part of pending prior U.S.                patent application Ser. No. 14/253,628, filed Apr. 15,                2014 by Neurometrix, Inc. and Shai Gozani et al. for                TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH                AUTOMATIC DETECTION OF USER SLEEP-WAKE STATE (Attorney's                Docket No. NEURO-65), which claims benefit of:                -   (1) prior U.S. Provisional Patent Application Ser.                    No. 61/811,864, filed Apr. 15, 2013 by Neurometrix,                    Inc. and Shai Gozani for TRANSCUTANEOUS ELECTRICAL                    NERVE STIMULATOR WITH AUTOMATIC DETECTION OF PATIENT                    SLEEP-WAKE STATE (Attorney's Docket No. NEURO-65                    PROV);            -   (c) claims benefit of prior U.S. Provisional Patent                Application Ser. No. 61/819,159, filed May 3, 2013 by                Neurometrix, Inc. and Thomas Ferree et al. for TAP                DETECTOR WITH HIGH SENSITIVITY AND SPECIFICITY FOR A                WEARABLE TRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR                (Attorney's Docket No. NEURO-66 PROV); and            -   (d) claims benefit of prior U.S. Provisional Patent                Application Ser. No. 61/858,150, filed Jul. 25, 2013 by                Neurometrix, Inc. and Andres Aguirre et al. for MOVEMENT                REGULATED TRIP CONDITIONS IN A WEARABLE TRANSCUTANEOUS                ELECTRICAL NERVE STIMULATOR (Attorney's Docket No.                NEURO-67 PROV);        -   (iii) claims benefit of prior U.S. Provisional Patent            Application Ser. No. 62/021,807, filed Jul. 8, 2014 by            Neurometrix, Inc. and Xuan Kong et al. for MEASURING TENS            DEVICE ON-SKIN TIME TO PREVENT AND MINIMIZE SKIN IRRITATION            (Attorney's Docket No. NEURO-73 PROV);    -   (B) claims benefit of prior U.S. Provisional Patent Application        Ser. No. 62/213,978, filed Sep. 3, 2015 by Neurometrix, Inc. and        Thomas Ferree et al. for TRANSCUTANEOUS ELECTRICAL NERVE        STIMULATOR WITH AUTOMATIC DETECTION OF LEG ORIENTATION AND        ROTATION FOR ENHANCED SLEEP ANALYSIS (Attorney's Docket No.        NEURO-77 PROV); and    -   (C) claims benefit of prior U.S. Provisional Patent Application        Ser. No. 62/101,029, filed Jan. 8, 2015 by Neurometrix, Inc. and        Shai Gozani et al. for METHOD AND APPARATUS FOR USING        TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION TO AID SLEEP        (Attorney's Docket No. NEURO-69A PROV);

(3) claims benefit of pending prior U.S. Provisional Patent ApplicationSer. No. 62/361,693, filed Jul. 13, 2016 by Neurometrix, Inc. and ThomasC. Ferree et al. for DYNAMIC CONTROL OF TENS THERAPY USING CONTINUOUSSLEEP DETECTION (Attorney's Docket No. NEURO-82 PROV).

The eighteen (18) above-identified patent applications are herebyincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to Transcutaneous Electrical NerveStimulation (TENS) devices that deliver electrical currents across theintact skin of a user via electrodes so as to provide symptomatic reliefof pain. More specifically, this invention relates to a TENS device wornduring sleep, and a method for controlling the timing and the intensityof TENS therapeutic stimulation based on continuous real-time sleepanalysis.

BACKGROUND OF THE INVENTION

Chronic pain due to diabetic neuropathy and other causes can interferewith sleep, which carries a host of secondary complications.Transcutaneous electrical nerve stimulation (TENS) devices provide painrelief by stimulating sensory nerves, which leads to an increase inendogenous opioids and down-regulation of pain signal transmission tothe brain.

The most common form of TENS is commonly referred to as “conventionalTENS”. With a conventional TENS device, an electrical circuit generatesstimulation current pulses with specified characteristics. The pulsewaveform characteristics include intensity (mA), duration (μsec) andshape (typically monophasic or biphasic). The pulse patterncharacteristics include the frequency (Hz) of the stimulation pulses andthe length of each continuous stimulation session (minutes). Theseparameters are correlated to the therapeutic dose. For example, higheramplitude and longer pulses (i.e., larger pulse charge) increase thedose, whereas shorter stimulation sessions decrease the dose. Clinicalstudies suggest that pulse charge and stimulation session duration havethe greatest impact on therapeutic dose.

Electrical stimulation is typically delivered to the user throughelectrodes, with the electrical stimulation being in the form of lowintensity (typically less than 100 mA), short duration (typically 50-400μsec) pulses at frequencies typically between about 10 and 200 Hz. Theelectrodes are placed on the skin of the user. The electrodes typicallyutilize hydrogels to create a stable low-impedance electrode-skininterface to facilitate the delivery of electrical current to the userso as to stimulate peripheral sensory nerves, whereby to suppress pain.

Poor sleep quality is one of the major causes of morbidity in patientssuffering from chronic pain [Fishbain D A, Hall J, Meyers A L, GonzalesJ, Mallinckrodt C. Does pain mediate the pain interference with sleepproblem in chronic pain? Findings from studies for management ofdiabetic peripheral neuropathic pain with duloxetine. J Pain SymptomManage. December 2008; 36(6):639-647]. It is, therefore, desirable forchronic pain sufferers to have the option of receiving TENS therapyduring sleep. In fact, several studies have shown that TENS therapy canimprove sleep quality (see, for example, Barbarisi M, Pace M C,Passavanti M B, et al. Pregabalin and transcutaneous electrical nervestimulation for postherpetic neuralgia treatment. Clin J Pain. September2010; 26(7):567-572).

A TENS device which could be used during sleep would offer uniqueopportunities to provide pain relief during bedtime with the goal ofimproving sleep. However, most TENS devices are designed to operateexclusively during the day (i.e., wake state) without any nighttime(i.e., sleep state) operation. This limitation is evident in the designof conventional TENS devices, in which the electric current is deliveredby a stimulator through wires (called leads) that are connected toelectrode pads on the skin. Such a design is not practical or safe foruse during sleep because the leads are cumbersome and may get tangled orpulled, and because the electrode pads can potentially peel off the skin(which will terminate TENS therapy) or, perhaps worse, can potentiallypartially peel off the skin, leading to increased current density andnegative consequences for the user (e.g., discomfort or, in extremecases, burns).

In prior U.S. patent application Ser. No. 14/230,648, filed Mar. 31,2014 by NeuroMetrix, Inc. and Shai Gozani et al. for DETECTING CUTANEOUSELECTRODE PEELING USING ELECTRODE-SKIN IMPEDANCE (Attorney's Docket No.NEURO-64), issued as U.S. Pat. No. 9,474,898 on Oct. 25, 2016, whichpatent is hereby incorporated herein by reference, there is disclosed anovel TENS device which allows TENS therapy to be applied duringnighttime (i.e., during sleep state) as well as during the day (i.e.,wake state). The key design elements that make this novel TENS devicesuitable for use during sleep are (1) the leads are eliminated becausethe electrode pads are attached directly to the housing containing theTENS stimulation circuitry, (2) the TENS housing and electrode pads areheld reliably and comfortably against the skin by an adjustable strap orband, (3) the TENS device continuously measures skin-electrode contactimpedance (and related electrical parameters) so as to detect if theelectrode pads peel (completely or partially) off the skin and the TENSdevice stops delivering current if peeling is detected, (4) therapeuticstimulation may be scheduled in one-hour on-off blocks so as to providepain relief throughout the night, and (5) the TENS device detects whenthe user is asleep and reduces the therapeutic stimulation levelautomatically so as not to disturb sleep.

The novel TENS device disclosed in prior U.S. patent application Ser.No. 14/230,648, filed Mar. 31, 2014 by NeuroMetrix, Inc. and Shai Gozaniet al. for DETECTING CUTANEOUS ELECTRODE PEELING USING ELECTRODE-SKINIMPEDANCE (Attorney's Docket No. NEURO-64), issued as U.S. Pat. No.9,474,898 on Oct. 25, 2016, which patent is hereby incorporated hereinby reference, is designed to be located on the upper calf of the user.This is for three reasons. First, the TENS device needs to stimulatesensory nerve fibers in order to provide widespread pain relief throughthe systemic effect of an increase in endogenous opioids anddown-regulation of pain signal transmission. The upper calf area has acluster of sensory nerve fibers that can be activated easily with atranscutaneous electrical nerve stimulator because of their proximity tothe surface of the skin. Second, some forms of chronic pain (such asthat due to diabetic neuropathy) are experienced most acutely in thefeet, and in addition to the mechanism of pain suppression throughendogenous opioids described above (which is systemic), there is alsoevidence for additional mechanisms of pain suppression that are morelocal, thus making it advantageous to place the TENS device on the uppercalf of the user. Third, chronic pain can be persistent throughout theday, often worsening at night, and wearing the TENS device on the uppercalf makes it discreet and unobtrusive, which encourages more regularuse.

In pending prior U.S. patent application Ser. No. 14/253,628, filed Apr.15, 2014 by NeuroMetrix, Inc. and Shai Gozani et al. for TRANSCUTANEOUSELECTRICAL NERVE STIMULATOR WITH AUTOMATIC DETECTION OF USER SLEEP-WAKESTATE (Attorney's Docket No. NEURO-65), published as U.S. PatentApplication Publication No. US 2014/0309709 on Oct. 16, 2014, whichpatent application is hereby incorporated herein by reference, there isdisclosed a TENS device which is designed for use during sleep. ThisTENS device detects when the user is asleep and adjusts the therapeuticstimulation level to optimize therapy according to user preferences andsimultaneously to avoid disturbing sleep.

In pending prior U.S. patent application Ser. No. 14/980,041, filed Dec.28, 2015 by NeuroMetrix, Inc. and Thomas Ferree et al. forTRANSCUTANEOUS ELECTRICAL NERVE STIMULATOR WITH AUTOMATIC DETECTION OFLEG ORIENTATION AND LEG MOTION FOR ENHANCED SLEEP ANALYSIS, INCLUDINGENHANCED TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION (TENS) USING THESAME (Attorney's Docket No. NEURO-77), published as U.S. PatentApplication Publication No. US 2016/0144174 on May 26, 2016, whichpatent application is hereby incorporated herein by reference, a novelTENS device is disclosed which may be used to improve sleep quality andto also quantify sleep quality and sleep disorders, since users will bemore likely to use the TENS device if they are aware of, and convincedof, its benefit to their sleep.

The gold standard in determining the sleep-wake state of a subject ispolysomnography which comprises at least three distinct types of data,i.e., electroencephalogram (EEG), electrooculography (EOG) andelectromyography (EMG). Because of the difficulty in recording andanalyzing these types of data, actigraphy has been developed and refinedover the last 30 years as a practical alternative to study sleep/awakepatterns. Actigraphy is a continuous recording of body movement by meansof a body-worn device, typically equipped with accelerometers[Ancoli-Israel S, Cole R, Alessi C, Chambers M, Moorcroft W, Pollak C P.The role of actigraphy in the study of sleep and circadian rhythms.Sleep. May 1 2003; 26(3):342-392].

Wearable electronic devices for health and fitness have becomewidespread, and most have accelerometers and, from acceleration data,compute various metrics of activity to track daytime activities and/orto quantify sleep patterns. Most of these actigraphy-based devices areworn on the wrist however, and in certain ways that limits their abilityto detect and quantify sleep.

Significantly, it has now been recognized that the placement of a novel,accelerometer-equipped TENS device on the upper calf of a user, withtight mechanical coupling to the upper calf of the user, may be used tosupport novel approaches for detecting when the user is asleep, andnovel metrics for analyzing the sleep of the user, and novel means toquantify body and leg motions associated with poor sleep quality and/ordisorders such as restless leg syndrome, and novel methods for providingenhanced TENS therapy using the same. Among these novel metrics are “legmovements”, “body roll events” associated with rolling over in bed, and“time-on-back” data which is relevant to users suffering not only fromchronic pain, but also from problematic sleep positions which can causesnoring or sleep apnea. In addition to tracking and reporting such sleepindicators, real-time feedback to the user, based on indicator trends,can also help the user to improve sleep quality. By way of example butnot limitation, the novel device may be configured to provide an alert(e.g., via mechanical or electrical means on TENS device 100 or via asmartphone or another connected device) to the user when thetime-on-back duration exceeds a threshold. By way of further example butnot limitation, the novel device may be configured to modify TENSstimulation parameters when leg movement patterns associated withdiscomfort caused by nighttime pain are detected in order to enhance theanalgesic effect of TENS therapy.

SUMMARY OF THE INVENTION

The preferred stimulation parameters for TENS therapy may be differentduring the day than the preferred stimulation parameters at night. Forexample, a lower stimulation intensity is generally preferred at night(i.e., during sleep) so as to decrease the likelihood that TENSstimulation interferes with sleep. Users may also achieve adequateanalgesia with shorter stimulation sessions and/or longer inter-sessionsintervals.

It may also be desirable for TENS parameters to be adaptively adjustedin real-time based on a user's sleep characteristics. The presentinvention discloses a method for adjusting TENS parameters adaptivelybased on the user's sleep patterns. Other measurements that may be usedto modify overnight TENS parameters include, but are not limited to,user skin temperature and temperature changes, skin impedance andimpedance changes, heart rate and heart rate variability,electroencephalograph (EEG) patterns and pattern changes, breathingpatterns and pattern changes, and/or electrooculography (EOG)characteristics and patterns.

Thus, the present invention comprises the provision and use of a novelTENS device which comprises a TENS stimulator designed to be placed onthe user's upper calf (or other anatomical location) and apre-configured electrode array designed to provide circumferentialstimulation to at least one nerve within the upper calf of the user (orother anatomical location). A three-axis accelerometer incorporated intothe TENS device measures the projection of static gravity onto eachaxis, which depends on body orientation, and the time-varyingacceleration on each axis, due to linear or rotational motion of thebody. Acceleration is measured in units of g (standard earth gravity).Alternatively and/or additionally, a three-axis gyroscope can beincorporated into the TENS device and can provide information aboutorientation and rotational motion of the body.

The placement of the novel TENS device on the upper calf of the usersupports novel approaches for detecting when the user is asleep, and forquantifying sleep and assessing abnormal body and leg motions, and forproviding enhanced TENS therapy using such sleep analysis.

First, the novel TENS device measures leg orientation, which is highlycorrelated with body orientation and therefore indicative of the user'srecumbent state (and thereby the user's sleep-wake state). Specifically,the novel TENS device measures two distinct aspects of leg orientation:leg “elevation” (or the angle of the lower leg relative to thehorizontal), and leg “rotation” (or the angle of rotation of the lowerleg about its own axis).

Second, the novel TENS device measures leg motion, which is alsoindicative of the user's sleep-wake state. Specifically, the novel TENSdevice measures two distinct aspects of leg motion: “net activity”(which is the magnitude of movement-related acceleration averaged withinone-minute windows), and “leg movements” (or brief events that are knownto occur in sleep but are not evident in net activity). Some legmovements accompanied by a large leg rotation may be further classifiedas “body roll events” (such as occur when rolling over in bed).Repetitive leg movements may occur in people with chronic pain and othermedical conditions, and may degrade the quality of sleep experienced bythe person (and his/her sleep partner). Quantification and monitoring ofthe repetitive leg movements may provide insights to these conditionsand trends of these conditions.

Third, the novel TENS device combines these two measures of legorientation (i.e., leg elevation and leg rotation) and two measures ofleg motion (i.e., net activity and leg movements) to improve sleepquantification and to utilize more precise quantification metrics toenhance therapeutic benefits.

Based on body activity, elevation, and/or position measurements, TENSstimulation parameters are adaptively adjusted to the user's sleepcharacteristics and the user's potential needs for TENS stimulationtherapy to control pain. To minimize nerve habituation, TENS is mosteffective if it is used according to a schedule which includesstimulation sessions and breaks between those stimulation sessions. Innormal daytime use, one-hour stimulation sessions are separated byone-hour breaks. In one embodiment of the present invention, thestimulation session duration is reduced from 60 minutes to 30 minutes ifthe user is asleep. In another embodiment of the present invention, thestimulation intensity is reduced by 2 dB if the user is determined to beasleep. In another embodiment of the present invention, the start of thenext scheduled session is delayed if the sleep can be characterized asrestful (not fragmented) in the recent past. In another embodiment ofthe present invention, no sessions start after the user is determined tobe asleep. Still other adaptive adjustments to the TENS stimulationparameters may be made based on the user's sleep characteristics and theuser's potential needs for TENS stimulation therapy to control pain.

In one preferred form of the present invention, there is providedapparatus for providing transcutaneous electrical nerve stimulation(TENS) therapy to a user, said apparatus comprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the user's body;

a stimulation unit for electrically stimulating at least one nerve ofthe user;

a sensing unit for (i) sensing the user's body movement and bodyorientation to determine whether the user is in an “out-of-bed” state ora “rest-in-bed” state, and (ii) analyzing the sleep characteristics ofthe user during said “rest-in-bed” state; and

a feedback unit for at least one of (i) providing the user with feedbackin response to said analysis of said sleep characteristics of the user,and (ii) modifying the electrical stimulation provided to the user bysaid stimulation unit in response to said analysis of said sleepcharacteristics of the user;

wherein said sleep characteristics comprise a likelihood measure of theuser's sleep quality.

In another preferred form of the present invention, there is provided amethod for applying transcutaneous electrical nerve stimulation to auser, said method comprising the steps of:

applying a stimulation unit and a sensing unit to the body of the user;

using said stimulation unit to deliver electrical stimulation to theuser so as to stimulate one or more nerves of the user;

analyzing electromechanical sensing data collected by said sensing unitin order to (i) determine the user's body orientation, and (ii) quantifybody activity levels so as to determine whether the user is in an“out-of-bed” state or a “rest-in-bed” state, whereby to determine thequality and duration of the user's sleep during the “rest-in-bed” state;and

modifying the electrical stimulation delivered by said stimulation unitbased on said sleep quality and said duration of the user's sleep duringthe “rest-in-bed” state.

In another preferred form of the present invention, there is providedapparatus for monitoring the sleep patterns of a user, said apparatuscomprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the user's body;

a sensing unit carried by the housing for (i) sensing the user's bodymovement and body orientation to determine whether the user is in an“out-of-bed”state or a “rest-in-bed” state, and (ii) analyzing the sleepcharacteristics of the user during said “rest-in-bed” state; and

a feedback unit for providing the user with feedback in response to saidanalysis of said sleep characteristics of the user.

In another preferred form of the present invention, there is provided amethod for monitoring the sleep patterns of a user, said methodcomprising of the steps of:

applying a sensing unit and a feedback unit to the body of a user;

using said sensing unit to determine the user's body movement and bodyorientation to (i) determine whether the user is in an “out-of-bed”state or a “rest-in-bed” state, and (ii) analyze the sleepcharacteristics of the user during said “rest-in-bed” state; and

providing the user with feedback via said feedback unit in response tosaid analysis of said sleep characteristics of the user.

In another preferred form of the present invention, there is providedapparatus for providing transcutaneous electrical nerve stimulation(TENS) therapy to a user, said apparatus comprising:

a housing;

an application unit for providing mechanical coupling between saidhousing and the leg of a user;

a stimulation unit for electrically stimulating at least one nerve ofthe user; and

a sensing unit for (i) sensing the user's leg orientation and leg motionto determine whether the user is in an “out-of-bed” state or a“rest-in-bed state”, wherein sensing the user's leg orientationcomprises determining the user's leg elevation and leg rotation, andfurther wherein sensing the user's leg motion comprises determining theuser's net activity and leg movements, and (ii) analyzing the sleepcharacteristics of the user during said “rest-in-bed” state; and

a controller for modulating said stimulation unit based on saiddeterminations made by said sensing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a schematic view showing a novel TENS device formed inaccordance with the present invention, with the novel TENS device beingmounted to the upper calf of a user;

FIG. 2 is a schematic view showing the novel TENS device of FIG. 1 ingreater detail;

FIG. 3 is a schematic view of the novel TENS device shown in FIGS. 1 and2 attached to the tissue of a patient;

FIG. 4 is a schematic view of the novel TENS device of FIGS. 1 and 2,including its user state (i.e., out-of-bed and rest-in-bed) detector andsleep characteristics estimator;

FIG. 5 is a schematic view showing the on-skin detection system of thenovel TENS device shown in FIGS. 1 and 2, as well as its equivalentcircuits when the novel TENS device is on and off the skin of a user;

FIG. 6 is a schematic view showing the orientation of the accelerometerincorporated in the novel TENS device of FIGS. 1 and 2, when the novelTENS device of FIG. 1 is applied to the upper calf of a user;

FIG. 7 is a schematic view showing the relationship betweengravitational force vector g and the accelerometer y-axis in the novelTENS device when the novel TENS device (applied to upper calf of theuser) rests at an elevation angle θ with respect to the horizontalplane;

FIG. 8 is a schematic view showing the detection of a leg movement (LM)event, and calculation of the change Δφ in device rotational angle φafter (vs. before) the LM event;

FIG. 9 is a schematic view showing the mathematics for relating theaccelerometer rotational angle φ (measured by the accelerometer) to theleg rotational angle β, via a third angle α representing the rotationalposition of the novel TENS device on the upper calf of a user; and

FIG. 10 is a schematic flow chart showing exemplary operation of thenovel TENS device, including its user state detector.

FIG. 11 is a schematic view showing accelerometer data being processedby various components of the sensing unit in order to determine segmentsof data in an “out-of-bed” (OOB) state and a “rest-in-bed” state.

FIG. 12 is a schematic view showing that the sleep probability ofaccelerometer data epochs increases with time within the “rest-in-bed”state, with each subplot of sleep probability being characterized by themean leg activity feature A and mean leg elevation angle feature θ asdetermined by processing the accelerometer data; and

FIG. 13 is a schematic view showing exemplary operation of the novelTENS device, including its user state (i.e., “out-of-bed” state and“rest-in-bed” state), fragmented sleep quality (poor sleep quality)indicator, and modification of the TENS therapy session start time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The Novel TENS Devicein General

FIG. 1 illustrates a novel TENS device 100 formed in accordance with thepresent invention, with the novel TENS device being shown worn on auser's upper calf 140. A user may wear TENS device 100 on either leg ora user may wear one TENS device 100 on each leg.

TENS device 100 is shown in greater detail in FIG. 2 and preferablycomprises three primary components: a stimulator 105, a strap 110, andan electrode array 120 (comprising a cathode electrode and an anodeelectrode appropriately connected to stimulator 105 as is well known inthe art). Stimulator 105 preferably comprises three mechanically andelectrically inter-connected compartments 101, 102, and 103.Compartments 101, 102, 103 are preferably inter-connected by hingemechanisms 104 (only one of which is shown in FIG. 2), thereby allowingTENS device 100 to conform to the curved anatomy of a user's leg. In apreferred embodiment of the present invention, compartment 102 housesthe TENS stimulation circuitry (except for a battery) and user interfaceelements 106 and 108. Compartment 102 also houses an accelerometer 152and a gyroscope 163 (see FIG. 4), preferably in the form of asemiconductor chip comprising the accelerometer and gyroscope, fordetecting user gestures, user leg and body orientation, and user leg andbody motion, as will hereinafter be discussed. Compartment 102 alsohouses a real-time clock 505 (FIG. 4). In a preferred embodiment,compartments 101 and 103 are smaller, auxiliary compartments that housea battery for powering the TENS stimulation circuitry and othercircuitry, and other ancillary elements, such as an ambient light sensoror detector 510 (FIGS. 4 and 6) for determining ambient lightconditions, and a wireless interface unit of the sort well known in theart (not shown) for allowing TENS device 100 to wirelessly communicatewith other elements (e.g., a hand-held electronic device such as asmartphone 860). In another embodiment of the present invention, onlyone or two compartments may be used for housing all of the TENSstimulation circuitry, battery, and other ancillary elements of thepresent invention. In another embodiment of the present invention, agreater number of compartments are used, e.g., to conform better to thebody and to improve user comfort. In another embodiment of the presentinvention, a flexible circuit board is used to distribute the TENSstimulation circuitry and other circuitry more evenly around the leg andthereby reduce bulk.

A temperature sensor 107 (FIG. 2) is embedded in (or attached to) thestrap 110 in order to measure the skin temperature of the user and themeasured skin temperature is electrically communicated to the stimulator105. In another embodiment, temperature sensor 107 is housed incompartment 102 (or one of the other compartments 101, 103).

Still looking now at FIG. 2, user interface element 106 preferablycomprises a push button for user control of electrical stimulation, anduser interface element 108 preferably comprises an LED for indicatingstimulation status and for providing other information to the user.Although a single LED is shown, interface element 108 may comprisemultiple LEDs of different colors. Additional user interface elements(e.g., an LCD display, audio feedback through a beeper or voice output,haptic devices such as a vibrating motor, etc.) are also contemplatedand are within the scope of the present invention.

The preferred embodiment of the present invention is designed to be wornon the upper calf 140 of the user as shown in FIG. 1. TENS device 100,comprising stimulator 105, electrode array 120, and strap 110, issecured to upper calf 140 by placing the apparatus in position and thentightening strap 110. Although the preferred embodiment of the presentinvention comprises placement of the TENS device on the upper calf ofthe user, additional anatomical locations (such as above the knee, onthe lower back, and on the upper arm) are also contemplated and are alsoconsidered to be within the scope of the present invention. In addition,it should also be appreciated that, if desired, multiple TENS devices100 may be worn by a user simultaneously (e.g., one TENS device 100 oneach upper calf 140 of the user, one TENS device 100 on the upper calf140 of a user and another TENS device 100 on the lower back of the user,etc.).

FIG. 3 is a schematic representation of the current flow between TENSdevice 100 and the user. As seen in FIG. 3, stimulation current 415 froma constant current source 410 flows into the user's tissue 430 (e.g.,the user's upper calf) via anode electrode 420. Anode electrode 420comprises a conductive backing (e.g., silver hatch) 442 and hydrogel444. The current passes through the user's tissue 430 and returns toconstant current source 410 through cathode electrode 432 (cathodeelectrode 432 also comprises a conductive backing 442 and hydrogel 444).Constant current source 410 preferably provides an appropriate biphasicwaveform (i.e., biphasic stimulation pulses) of the sort well known inthe art of TENS therapy. In this respect it should be appreciated thatthe designation of “anode” and “cathode” electrodes is purely notationalin the context of a biphasic waveform (i.e., when the biphasicstimulation pulse reverses its polarity in its second phase of thebiphasic TENS stimulation, current will be flowing into the user's bodyvia “cathode” electrode 432 and out of the user's body via “anode”electrode 420).

Further details regarding the construction and use of the foregoingaspects of TENS device 100 are disclosed in (i) U.S. Pat. No. 8,948,876,issued Feb. 3, 2015 to NeuroMetrix, Inc. and Shai N. Gozani et al. forAPPARATUS AND METHOD FOR RELIEVING PAIN USING TRANSCUTANEOUS ELECTRICALNERVE STIMULATION (Attorney's Docket No. NEURO-5960), which patent ishereby incorporated herein by reference, and (ii) prior U.S. patentapplication Ser. No. 14/230,648, filed Mar. 31, 2014 by Shai N. Gozaniet al. for DETECTING CUTANEOUS “ELECTRODE PEELING” USING ELECTRODE-SKINIMPEDANCE (Attorney's Docket No. NEURO-64), issued as U.S. Pat. No.9,474,898 on Oct. 25, 2016, which patent is hereby incorporated hereinby reference.

The User State Detector

In accordance with the present invention, TENS device 100 furthercomprises (e.g., within compartment 102) user state detector 500 for (i)determining the sleep-wake state of the user (i.e., for determiningwhether a user is in an “out-of-bed” state or a “rest-in-bed” state),(ii) analyzing the sleep of the user, and/or (iii) providing enhancedtranscutaneous electrical nerve stimulation (TENS) using the same. Tothis end, and looking now at FIG. 4, user state detector 500 generallycomprises the aforementioned accelerometer 152, the aforementionedgyroscope 163, the aforementioned real-time clock 505, theaforementioned temperature sensor 107, the aforementioned ambient lightdetector 510, a processor 515 for calculating user activity (e.g., bodyorientation, body movement and activity levels) and sleep quality, and acontroller 520 for modifying the operation of the constant currentsource 410 of TENS device 100 so as to provide customized and adaptiveTENS stimulation in accordance with determinations made by processor515. It will be appreciated that processor 515 preferably comprises amicroprocessor of the sort well known in the art having appropriatesoftware programming for providing the functions herein disclosed. Itwill also be appreciated that controller 520 preferably comprises aprogrammable controller of the sort well known in the art forcontrolling operation of the TENS stimulator as discussed herein.

When the TENS device is secured in position on the user's upper calf,the position and orientation of accelerometer 152 and gyroscope 163(FIG. 4) of TENS device 100 is fixed relative to the lower limb of theuser. Tight mechanical coupling between TENS device 100 and lower limb140 allows movement of the user's lower limb to be accurately measuredby accelerometer 152 and/or gyroscope 163. Such tight mechanicalcoupling is preferably established through the aforementioned strap 110.Alternatively, tight mechanical coupling may be established throughother means, e.g., a flexible band encasing the TENS device. If desired,a tension gauge 109 (FIG. 1) may be provided on strap 110 to confirmthat a tight mechanical coupling is established between TENS device 100and upper calf 140.

Data from accelerometer 152 and gyroscope 163 are analyzed in real timeby processor 515 of user state detector 500 to determine the orientationand motion of the lower limb (i.e., upper calf 140) of the user. Theorientation, motion, and activity level of the lower limb (i.e., uppercalf 140) of the user, determined by analyzing the data fromaccelerometer 152 and/or gyroscope 163 (or a combination of data fromboth accelerometer 152 and gyroscope 163), are used to determine thesleep-wake state, sleep patterns, and sleep characteristics of the user.Based on the sleep-wake state, sleep patterns, and sleep characteristicsof the user, TENS device 100 can modify its stimulation pattern (such asthe stimulation intensity level and the onset of the stimulation) viacontroller 520, or provide the user with additional feedback (such asmechanical vibration if the duration of the sleep-on-back state exceedsa threshold), or postpone the pre-programmed auto-start of the next TENStherapy session (e.g., if the user is determined to be in a state of“sound sleep” or “sleep without fragmentation”). In another form of thisinvention, data from gyroscope 163 are used to determine leg orientationand motion, particularly rotational motion, in order to determine thesleep pattern and/or sleep characteristics of the user.

The leg orientation and leg motion components measured by the user statedetector 500 of the present invention may individually or collectivelycontribute to the determination of the sleep-wake state and/or sleepcharacteristics of the user. In one preferred form of the invention,processor 515 of TENS device 100 measures the calf orientation of theuser, which is highly correlated with the body orientation of the user.More particularly, upright body orientation is generally a reliableindicator that the user is in a wake state, while recumbent orientationsuggests a resting state (e.g., such as occurs during a sleep or“rest-in-bed” state). Regular and robust body movement is more likelythe result of user activities during the daytime (e.g., walking duringan “out-of-bed” or “wake” state), while quiet or low-level spontaneousmovements are more likely during nighttime (e.g., spontaneous legmovement during a “rest-in-bed” or “sleep” state). Interactions of bodyorientation and movement level can also be useful in identifying thesleep-wake state of the user (i.e., thereby enhancing a sleep-wake stateclassification). Specifically, recumbent body orientation and alow-level of physical activity is generally a good indicator that theuser is asleep, while a consistent and repeated movement of the user'sleg while in an upright orientation is a reliable indicator that theuser is out of bed (i.e., in a “wake” state).

In addition, real-time clock 505 of user state detector 500 allowsassigning a nontrivial a priori probability of the sleep-wake state atany given time of the day in order to further refine the sleep-wakestate classification results obtained by the aforementioned analysis ofleg orientation and leg motion data (i.e., a user is more likely to beasleep at 3:00 am and less likely to be asleep at 4:00 pm). In apreferred embodiment of the present invention, to reflect that the apriori probability that the sleep state is low at a specific daytimewindow (even when the activity and orientation data suggest that theuser is in “rest-in-bed” state), the threshold value for classifyinguser body orientation as recumbent can be made more stringent.

In another embodiment of the present invention, output from ambientlight sensor 510 is used to improve sleep-wake classification results.The ambient light sensor 510 can be used to determine if the user is inan environment which has an illuminated or non-illuminated ambience, toreflect the a priori probability that a user is more likely to besleeping in a dark setting than in a brightly lit setting. Accordingly,the threshold values for classifying user body position and motion levelcan be adjusted to reflect the a priori probability of sleep.

In another embodiment of the present invention, output from bodytemperature sensor 107 is used to improve sleep pattern classificationresults. It has been recognized that body temperature fluctuates withdifferent sleep stages. In particular, body temperature tends to dropafter the onset of sleep (i.e., “stage 2” of sleep, when a user is nolonger conscious of their surroundings). Incorporating a skintemperature measurement into the sleep monitoring function of TENSdevice 100 improves the accuracy of the classification of sleep stagesand determination of sleep quality made by TENS device 100 (i.e., byprocessor 515 of TENS device 100).

On-Skin Detector

In one preferred form of the invention, TENS device 100 may comprise anon-skin detector to confirm that TENS device 100 is firmly seated on theskin of the user.

More particularly, the orientation and motion measures fromaccelerometer 152 and/or gyroscope 163 of TENS device 100 only becomecoupled with the orientation and motion of a user when the TENS deviceis worn by the user. In a preferred embodiment, an on-skin detector 521is provided to determine whether and when TENS device 100 is securelyplaced on the user's upper calf. In the preferred embodiment, andlooking now at FIG. 5, on-skin detector 521 may be provided within TENSdevice 100. More particularly, in one preferred form of the invention, avoltage of 20 volts from voltage source 204 is applied to the anodeterminal 212 of TENS stimulator 105 by closing the switch 220. If theTENS device is worn by the user, then user tissue 430, interposedbetween anode electrode 420 and cathode electrode 432, will form aclosed circuit to apply the voltage to the voltage divider circuitformed by resistors 208 and 206. More particularly, when TENS device 100is on the skin of the user, the equivalent circuit 260 shown in FIG. 5represents the real-world system and equivalent circuit 260 allows theanode voltage V_(a) 204 to be sensed through the voltage dividerresistors 206 and 208. The cathode voltage measured from the amplifier207 will be non-zero and close to the anode voltage 204. On the otherhand, when TENS device 100 is not on the skin of the user, theequivalent circuit 270 represents the real-world system and the cathodevoltage from amplifier 207 will be zero.

On-skin detector 521 is preferably employed in two ways.

First, if on-skin detector 521 indicates that electrode array 120 ofTENS device 100 has become partially or fully detached from the skin ofthe user, TENS device 100 can stop applying TENS therapy to the user.

Second, if on-skin detector 521 indicates that electrode array 120 ofTENS device 100 has become partially or fully detached from the skin ofthe user, processor 515 of TENS device 100 will recognize that the datafrom accelerometer 152 and/or gyroscope 163 may not reliably reflectuser leg orientation and leg motion, and user state detector 500 cantake appropriate action (e.g., alert the user). In this respect itshould be appreciated that, when the on-skin detector 521 indicates thatTENS device 100 is on the skin of the user, and accelerometer 152 and/orgyroscope 163 is closely coupled to the lower limb of the user, the datafrom accelerometer 152 and/or gyroscope 163 may be representative ofuser leg orientation and user leg motion. However, when the on-skindetector 521 indicates that TENS device 100 is not on the skin of theuser, accelerometer 152 and/or gyroscope 163 is not closely coupled tothe lower limb of the user, and the data from accelerometer 152 and/orgyroscope 163 will not be representative of user leg orientation anduser leg motion.

Electromechanical Sensor Data Processing

In one preferred form of the invention, user state detector 500comprises a processor 515 for taking the accelerometer data fromaccelerometer 152 and calculating user activity (e.g., body orientation,body movement and activity levels). In another form of the invention,data from gyroscope 163 are used by processor 515 to calculate useractivity. In another form of the invention, data from both accelerometer152 and gyroscope 163 are combined and used by processor 515 in order tocalculate user activity and body orientation, especially transitions inbody orientation from one position to another position.

More particularly, in one preferred form of the invention, processor 515uses the accelerometer data from accelerometer 152 and/or data fromgyroscope 163 to measure the user's leg orientation, which is highlycorrelated with body orientation and therefore indicative of the user'srecumbent state (and therefore the user's “rest-in-bed” state); andprocessor 515 uses the accelerometer data from accelerometer 152 tomeasure the user's leg motion, which is also indicative of the user'ssleep-wake state and leg motion activity levels; and processor 515 usesthe determinations of user leg orientation and user leg motion toenhance sleep characterization accuracy.

More particularly, processor 515 uses the accelerometer data fromaccelerometer 152 to measure two distinct aspects of the user's legorientation: leg “elevation” (or the angle of the lower leg relative tothe horizontal plane), and leg “rotation” (or the angle of rotation ofthe lower leg about its own axis). Measurement data provided toprocessor 515 from gyroscope 163 are especially useful in detecting andquantifying angular rotation of the user's leg about the axis of theuser's leg.

And processor 515 uses the accelerometer data from accelerometer 152 tomeasure two distinct aspects of leg motion: “net activity” (which is themagnitude of movement-related acceleration averaged within one-minutewindows), and “leg movements” (or brief events that are known to occurin sleep but are not evident in net activity). Some leg movementsaccompanied by a large leg rotation may be further classified as “bodyroll events” (such as occur when rolling over in bed).

Raw Data Stream at 50 Hz and 10 Hz.

In a preferred embodiment of the present invention, processor 515 forcalculating user activity (e.g., body orientation, body movement andactivity levels) is constructed and configured to operate as follows.Raw accelerometer data produced at 400 Hz are decimated to 50 Hz.Following that, the time scale of an “instant” is defined to be equal to0.1 sec. The 50 Hz data on each axis (x, y, z) are separately averagedover each instant, to provide a low-noise data stream at 10 Hz, denotedby A_(x)(t), A_(y)(t), and A_(z)(t).

Orientation Data Stream.

The accelerometer data A_(x)(t), A_(y)(t), and A_(z)(t) are used to formfeatures which are averages of A_(x)(t), A_(y)(t), and A_(z)(t) over alonger time window (e.g., a one minute window) to capture thesteady-state projection of earth gravity along each axis (x, y, z).These features are used for detecting leg orientation (i.e., legelevation and leg rotation).

Activity Data Stream.

Additionally, the accelerometer data A_(x)(t), A_(y)(t), and A_(z)(t)are high-pass filtered to remove the static gravity component in orderto isolate acceleration components caused by leg movement. The high-passfilter has −3 dB point at 0.5 Hz. High-pass filtered accelerometer dataare denoted as Ã_(x)(t), Ã_(y)(t), and Ã_(z)(t).

Data from the gyroscope 163 are processed similarly to produce datastreams with difference sampling rates.

Leg Elevation Detection

In one preferred form of the invention, user state detector 500 isconfigured to detect leg elevation.

More particularly, in order to determine the “body orientation state”for the purpose of sleep monitoring, the present invention uses the legelevation, which is computed by processor 515 of user state detector500, based on measurement data from accelerometer 152 and/or gyroscope163 when TENS device 100 is placed on the user's upper calf 140 (FIG.1). In a preferred embodiment, and looking now at FIG. 6, accelerometer152 (and/or gyroscope 163) is located on the circuit board 151 of theTENS circuitry housed inside compartment 102, so that theaccelerometer's 3-axis directions, shown at 153 in FIG. 6 (i.e., x-axis,y-axis, z-axis), are known and fixed in relationship to the lower legwhen the TENS device is placed on the user's upper calf: the y-axis isaligned longitudinally along the longitudinal axis of the lower leg; thex-axis is disposed tangential to the surface of the lower leg andperpendicular to the y-axis, and the z-axis points radially away fromthe surface of the lower leg.

A stationary upright user, or one sitting with feet resting on theground, will have an upright calf elevation. Consequently, the y-axisacceleration of accelerometer 152 will have a value of about −1 g due toEarth gravity 154 (FIG. 6), where g is the acceleration due to Earthgravity. The above measurement holds true regardless of the exactrotational position 160 of compartment 102 around upper calf 140. WhenTENS device 100 is placed upside down on the upper calf, which is apossible placement position, the accelerometer axes rotate as shown at155 in FIG. 6. In this case, a stationary upright user will have ameasured acceleration value along the y-axis of about +1 g. By contrast,a stationary recumbent user lying with legs elevated on a bed will havea measured acceleration value along the y-axis of about 0 g. In apreferred embodiment, if the absolute value of the y-axis accelerationmeasurement is greater than a threshold level, then the leg elevation isconsidered to be upright, otherwise the leg elevation is considered tobe recumbent.

Looking now at FIG. 7, where the Earth's gravitational vector isdownward, the elevation angle θ (172) represents the angle between thepositive accelerometer y-axis direction (174) and the true horizontalplane (170). In a preferred embodiment, the y-axis accelerationmeasurement threshold level is set to 0.50 g, corresponding to a legelevation angle θ≈30° from the horizontal plane, however, otherthreshold values may also be used, and users may have the option ofadjusting this value to better distinguish their sleep and wakebehaviors.

In general, the acceleration measured along the y-axis will include notonly the projection of gravity onto that axis, but also a contributionfrom motion:

A _(y)(t)=±sin|θ(t)|+m(t)[in unit of g]

where t is time, and m(t) is the contribution due to leg motion. Thespecific ±sign depends upon the TENS device placement on upper calf 140and is fixed for each placement. The motion component m(t) is considered“noise” in the context of determining leg elevation, and will have zeromean over a sufficiently large window.

In a preferred embodiment, a leg elevation algorithm, taking intoaccount user body movement, is implemented by processor 515 of userstate detector 500 (i.e., to determine whether the user is in an“out-of-bed” state when the user is upright or whether the user is in a“rest-in-bed” state when the user is recumbent) in the following manner.

Step 1. Set a target angle threshold θ₀ (this is the “Threshold1” shownat step 910 in FIG. 10) for the angle θ so that |θ|<θ₀ corresponds tothe case where the upper calf 140 of the user is recumbent. In apreferred embodiment, the target angle threshold θ₀ is set to 30°.

Step 2. Define non-overlapping windows of length N, called “epochs”. Thetime at the end of each epoch is denoted T. In a preferred embodiment,the accelerometer data (in units of g, standard earth gravity) aresegmented into epochs, i.e., one-minute windows. With an accelerometerdata rate of 10 Hz, the epoch length is N=600. The mean A_(y,T) and thestandard error of the mean SE_(Y,T) are calculated based on samples ineach epoch.

Step 3. Let θ_(T)=sin⁻¹A_(y,T). Values of θ_(T)≈θ₀ can lead to erraticswitching of the leg elevation state. In order to reduce this, define ahysteresis band θ₀±θ_(H). In the preferred embodiment, the hysteresisparameter θ_(H) is set to 2.5°, but other values are possible (butshould be small compared to θ₀). In the preferred embodiment, ratherthan computing sin⁻¹ for every epoch, the angular thresholds are insteadconverted to acceleration units, i.e., by computing two thresholdsA_(±)=sin(θ₀±θ_(H)), against which A_(y,T) will be compared.

Step 4. The ability of the hysteresis band to prevent erratic switchingof the leg elevation state depends upon the amount of noise in the data,characterized by SE_(Y,T), which is the standard error of the meanA_(y,T). In order to account for the noise level in the data, processor515 of user state (i.e., leg orientation and leg motion) detector 500,processor 515 compares the acceleration data A_(y,T) to the thresholdsA_(±). However, instead of comparing the mean A_(y,T) per se to thethresholds A_(±), processor 515 compares the “confidence interval”A_(y,T)±ηSE_(Y,T) to the thresholds A_(±). More specifically, for eachepoch, if the prior elevation state was recumbent, in order to classifythe next state as upright, processor 515 of user state detector 500requires [|A_(y,T)|−ηSE_(Y,T)]>A₊. If the prior elevation state wasupright, in order to classify the next state as recumbent, processor 515of user state detector 500 requires [|A_(y,T)|+ηSE_(Y,T)]<A⁻. In apreferred embodiment η=3, but other values are possible.

It should be appreciated that the hysteresis band is helpful asdescribed above, but in another form of the invention the hysteresisband is omitted, which is the same as setting its band θ_(H) to 0°.

Instantaneous Activity

In one preferred form of the invention, processor 515 of user statedetector 500 may be configured to detect instantaneous activity.

More particularly, when TENS device 100 is worn on the user's upper calf140, the user's activity will be captured by accelerometer 152 of theTENS device. Each axis (x, y, z) of accelerometer 152 measures theprojection of the acceleration vector along that axis. As describedabove, the measured acceleration includes the static effect of earthgravity, as well as contributions from leg movement. In order to isolatethe contributions from leg movement, processor 515 of user state (i.e.,leg orientation and leg motion) detector 500 high-pass filters theinstant data vector A(t)=[A_(x)(t),A_(y)(t),A_(z)(t)] before furtherprocessing.

Although the acceleration component for each individual axis of theaccelerometer contains unique and useful information for body movementanalysis, the vector magnitude of acceleration, called the“instantaneous acceleration”, denoted Ã_(I)(t) and defined in equationbelow, is commonly used to quantify the overall motion-related activity:

Ã _(I)(t)=√{square root over (Ã _(X)(t)² +Ã _(Y)(t)² +Ã _(Z)(t)²)}

In a preferred embodiment of the present invention, processor 515 ofuser state detector 500 uses this instantaneous acceleration Ã_(I)(t)for the actigraphy calculations. However, calculations based on othercombinations of acceleration axes may also be used. For example, ratherthan combining all three axes equally as done with Á_(I)(t) as definedabove, only some axes may be used, or certain axes may be contrastedthrough subtraction.

In another form of the invention, the y-axis acceleration data A_(y)(t)is analyzed to detect periodic patterns of movement that match walkingactivity patterns in order to determine if the user is walking. In yetanother form of the invention, data from gyroscope 163 (instead of, orin addition to, data from accelerometer 152) are used to detect periodicpatterns of movement that match walking activity patterns in order todetermine if the user is walking, since the angular rotation of theuser's leg with respect to the user's knee joint generally follows aperiodic pattern when the user is walking.

Leg Movement Detector

In one preferred form of the invention, processor 515 of user statedetector 500 may be configured to detect leg movement which is morelikely to occur during sleep when the user is determined to be in a“rest-in-bed” state.

More particularly, the instantaneous acceleration Ã_(I)(t) is a timeseries comprised of brief events, such as leg movements known to occurduring normal and abnormal sleep, and sustained activity, such as occursduring walking, running, or climbing stairs. In a preferred embodiment,leg movements (LM) are computed in a manner that is consistent with thedetection of periodic leg movements (PLM) defined in the clinicalliterature (Bonnet et al, 1993; Zucconi et al, 2006), however, otherapproaches to detecting brief leg movements are possible and areconsidered to be within the scope of the present invention.

In the preferred embodiment, a leg movement (LM) detection algorithm isimplemented by processor 515 of user state detector 500 in the followingmanner.

Step 1. Define two thresholds (these are the “Threshold2” and“Threshold3” shown at steps 914 and 918, respectively, in FIG. 10) thatthrough data analysis are found to be sensitive and specific to briefleg movements. In the preferred embodiment, and appropriate to thevariance properties of the data measured by the accelerometer 152, thesethresholds are 0.02 g (816 in FIG. 8) and 0.03 g (815 in FIG. 8), butother values may also be used.

Step 2. Define an instantaneous activity state (IAS) and initialize theIAS to False.

Step 3. Compute instantaneous acceleration Ã_(I)(t) for each timeinstant.

Step 3. Update the IAS for each time instant as follows. If IAS=Falseand Ã_(I)(t)>0.03 g, then set IAS=True. If IAS=True and Ã_(I)(t)<0.02 g,then set IAS=False. Two thresholds used in this way implement hysteresisin a simple way to prevent rapid switching in the IAS.

Step 4. When IAS becomes True, a leg movement (LM) period begins. WhenIAS becomes false and remains false for more than 0.5 second, the LMperiod ends. Thus a contiguous time interval in which IAS=True, andsurrounded by intervals in which IAS=False, comprises a leg movement(LM) period. However, if contiguous intervals for which IAS is True areseparated by less than 0.5 second, the brief interval for which IAS wasFalse is ignored.

The top panel (810) in FIG. 8 shows an example of the leg movement (LM)detection algorithm applied to real data. Time is measured in instants,i.e., steps of 0.1 second. The dots, and the line 812 connecting them,are the instantaneous accelerations Ã_(I)(t). The vertical line 813 iswhen Ã_(I)(t) first went above the threshold 815 (threshold value=0.03g), at which point IAS was set to True. The instantaneous accelerationsÃ_(I)(t) fell below the second threshold 816 (threshold value=0.02 g)before the 90^(th) instant. However, their durations were shorter than0.5 second so they were ignored and the LM period continued. Thevertical line 814 shows the instant when Ã_(I)(t) first went below thesecond threshold 816 for more than 0.5 second so the LM period wasterminated. The net result is an LM period with a duration of 89instants (i.e., 8.9 seconds).

Body Roll Detector

In one preferred form of the invention, processor 515 of user statedetector 500 is configured to function as a body roll detector when TENSdevice 100 determines that the user is in a “rest-in-bed” state.

More particularly, when the TENS device 100 (FIG. 9) is worn on thelower leg (i.e., upper calf 140) of a user, its accelerometer 152 willsense the projection of the gravity in its x-z plane when the user is ina recumbent position. The angle φ between the device x-axis and thegravity vector −g can be calculated based on the projected gravity valuein the x and z axis. Axis z′ is aligned with the “big toe” direction ofthe user's leg to which the TENS device 100 is attached. Angle α betweenthe device z-axis and the leg x′-axis is fixed when the TENS device issecurely placed on the lower leg (i.e., upper calf 140) of the user.Finally, the body orientation angle β defines the relative rotationalposition between the leg (defined as the direction in which the big toeis pointed, i.e., the z′-axis) and the earth gravity (z″-axis). Theangular value remains the same when measuring from the x′-axis to thex″-axis. It is straightforward to derive the relationship between β andφ as follows:

β=180−α−φ

Because the angle α is fixed, the leg rotation angle β can be derivedfrom the angle φ as measured by the accelerometer 152.

Some brief increases in activity that are classified as leg movement(LM) are associated with large changes in the rotational angle φmeasured by the TENS device 100. Rolls of sufficient magnitude areunlikely to involve only the leg, but rather are likely to indicate thatthe entire body is rolling over while in bed, e.g., from the left sideto the right side, or from the back to the left side or the right side.Some leg movements (LMs) may therefore be classified as “body rollevents”.

In one preferred embodiment, a body roll detection algorithm isimplemented by processor 515 in user state detector 500, using only theangle change Δφ, in the following manner:

Step 1. For each LM period detected, select the raw acceleration vectorA(t) in short windows before and after the leg movement. In a presentinvention, this window is an instant (0.1 seconds).

Step 2. Before and after each LM period, take the instant values of A(t)(not high-pass filtered) on each axis separately so as to obtainA_(x)(t), A_(y)(t), and A_(z)(t).

Step 3. Using these values before and after the LM, compute the rotationangle φ (t)=a tan 2{A_(x)(t), A_(z)(t)}. The inverse tangent function atan 2 returns an angle in the range −180°<φ(t)≦180°), i.e., a result inall four possible quadrants.

Step 4. Compute the change in rotational angle Δφ=φ_(after)−φ_(before).In order to facilitate comparison with a threshold (this is the“Threshold4” shown at step 924 in FIG. 10), this difference is put inthe range −180°<Δφ≦180°, i.e., if Δφ>180° then subtract 360°, but ifΔφ≦−180° then add 360°.

Step 5. Compare the absolute value |Δφ| with a threshold value. In thepresent invention, this threshold value is 50°, but other values may beused. If |Δφ|>50°, then classify the LM event as a “body roll event”.

The middle panel (820) in FIG. 8 shows this body roll detectionalgorithm applied to real data. The acceleration values A_(x)(t),A_(y)(t), and A_(z)(t) are plotted in traces 821, 822, and 823. They-axis component A_(y)(t)≈0 g throughout the event, consistent with thecondition that lower leg elevation is in recumbent state. In contrast,A_(x)(t) and A_(z)(t) show significant activities, especially betweentime instants 30 and 70. In addition, the steady state value forA_(x)(t) changed from +1 g (before the LM period) to −1 g (after the LMperiod), suggesting a body roll event.

The bottom panel (830) of FIG. 8 shows the calculation of the elevationangle θ (833) and the rotation angle φ (834) for each instant. Theelevation angle θ≈0 throughout the event, consistent with the lower legbeing in recumbent elevation. In contrast, the rotation angle φ changesfrom φ≈+90° (indicated by the empty circle 831) to φ≈−88° (indicated bythe filled circle 832). The angular change is Δφ≈178°, consistent with a(rightward) roll of the entire body.

These body rolls may be reported directly to the user to inform themabout their sleep patterns. In addition, because body roll events may bebrief, the associated increase in activity may not be evident in theepoch average of activity, and therefore may not cause that epoch to beclassified as awake. Although rolling over in bed may not indicate anawake state, it does indicate momentarily restless sleep. This novelapproach for detecting body rolls by evaluating changes in roll anglesassociated with brief leg movement (LM) permits the differentiation ofleg movement associated with no body rolls from leg movement associatedwith body rolls, and thus provides a finer description of sleep patternsthat are useful to the user and their healthcare providers.

In another preferred embodiment, rather than using single instants ofA(t) before and after the LM to compute the angles φ, the mean or medianvalues of A(t) over several instants before and after the LM are used toimprove robustness to noise.

In another preferred embodiment, a body roll detection algorithm isimplemented by processor 515 of user state detector 500 using the anglechange Δβ in the following manner. Consider a person lying on theirback, with the TENS device placed on their right leg. Recalling that,with the TENS device placed on either leg, β=0 when the toes are pointedvertically upward, and β increases with counterclockwise (CCW) rotation,therefore the most likely range of leg rotational positions is−80°≦β≦0°. Any change in angle Δβ that remains within that range may notlikely be associated with a body roll. In contrast, a change in angle Δβfrom inside that range to outside that range is most likely associatedwith a body roll. In this way, using the change in angle Δβ, thethreshold for detecting a body roll may be adjusted depending upon theleg on which the device is placed. That is to say, in addition to themagnitude of the change Δβ, the value of the leg rotation angle β beforeand after the leg movement (LM), and the sign of the angle change Δβacross the leg movement (LM), may be used to improve performance of thebody roll detector.

While analyses of accelerometer data based on earth gravity projectionprovide the steady state value of the rotational angles, it should beappreciated that gyroscope measurements (i.e., data from gyroscope 163)capture transient rotational activities such as angular acceleration andangular velocity. Processing of angular velocity data of the leg (e.g.,via processor 515 of user state detector 500 of TENS device 100) allowschanges in the leg rotation angle β to be directly determined. In onepreferred form of the invention, rotational angle changes derived frommeasurements (i.e., data) collected by gyroscope 163 can be used todetect and quantify a user's leg rotation events. In another form of theinvention, data from accelerometer 152 and data from gyroscope 163 arecombined together and processed by processor 515 of user state detector500 of TENS device 100 in order to improve the performance of the bodyroll detector.

Static Body Rotational Position Detector

In one preferred form of the invention, processor 515 of user statedetector 500 may be configured to function as a static body rotationalposition detector.

More particularly, users with sleep apnea are recommended to sleep noton their back.

Because of the limited rotational range of motion of the human hip, legrotational position is highly correlated with body position, e.g., whensleeping on one's back, the toes of either foot are pointed upward abovethe horizontal plane to varying degrees, not likely exactly on thehorizontal plane, and never below the horizontal plane. Thisobservation, together with the placement of the novel TENS device on theupper calf of the user, allows an innovative addition to sleep analysis.

The time scale of an “epoch” equal to one minute, and the epoch-averagednon-high-pass filtered acceleration values Ā_(X,T)(t), Ā_(Y,T)(t), andĀ_(Z,T)(t) were introduced above in the section entitled “Leg ElevationDetection”. Because it is sufficient to report the time spent sleepingon the back at the resolution of one minute, these epoch-averagedacceleration values may be advantageously used in the following mannerto detect static body rotational position.

Consistent with the roll detector definition of the rotational positionangle φ, let φ_(T)=a tan 2{Ā_(X,T)(t), Ā_(Z,T)(t)} as before, whereĀ_(X,T)(t) and Ā_(Z,T)(t) are raw (i.e., not high-pass filtered)accelerations averaged over an epoch T. Let β_(T)=the angle of the toesrelative to the vertical. The relation between φ_(T) and β_(T) dependsupon the rotational placement of the TENS device on the upper calf ofthe user, denoted α. Because the electrode gel 444 is sticky and thestrap 110 is supportive, the TENS device does not move on the user's legonce it is placed onto the upper calf 140, therefore the angle α isconstant as long as the TENS device is on the leg of the user.

Looking now at FIG. 9, the double-primed coordinate system (i.e., x″,y″, z″, with y″ not being seen in FIG. 9 since it extends down the axisof the leg) is fixed to the Earth with gravity along the vertical, thesingle-primed coordinate system (i.e., x′, y′, z′, with y′ not beingseen in FIG. 9 since it extends down the axis of the leg) is fixed tothe leg, and the unprimed coordinate system (i.e., x, y, z, with y notbeing seen in FIG. 9 since it extends down the axis of the leg) is fixedto the TENS device measuring A_(X,T)(t) and Ā_(Z,T)(t). The Earthcoordinate system has its z″-axis along the vertical, the leg coordinatesystem has its z′-axis in the direction of the toes, and the legrotational angle β is the angle between the Earth x″-axis and legx′-axis. The TENS device angle α is the location of the TENS device onthe leg measured from the leg x′-axis. Using knowledge of theaccelerometer axes in the TENS device, and standard techniques ofgeometry including the identification of similar triangles, it will beevident to those skilled in the art that these angles are related simplyby β=180−α−φ. In each epoch, therefore, these angles are related simplyby β_(T)=180−α−φ_(T).

In a preferred embodiment, the following simple procedure is used byprocessor 515 of user state detector 500 to determine whether the useris on-back through an estimation of the angle β when the user is in a“rest-in-bed” state.

Step 1. The user places the TENS device on the lower leg of the user andfastens the strap 110 snugly around their upper calf 140, lies recumbentwith the leg nearly horizontal, points their toes vertically upward, andremains still.

Step 2. The user indicates to the TENS device that the aforementionedconditions have been met. This indication may take the form of a seriesof button presses (e.g., with button 106), a series of taps oncompartment 102 detected by the accelerometer 152, or an indication on asmartphone 860 in communication with the TENS device 100.

Step 3: With the toes pointed upright, β≈0, therefore it is trivial toestimate {circumflex over (α)}180−{circumflex over (φ)} where{circumflex over (φ)} is estimated from accelerometer data acquiredduring the toe-up period. In order to facilitate calculations, put thisdifference in the range −180°<{circumflex over (α)}≦180°, i.e., if{circumflex over (α)}>180° then subtract 360°, but if {circumflex over(α)}≦−180° then add 360°.

Step 4: In every epoch ending at time T, use this value of {circumflexover (α)} to compute β_(T)=180−{circumflex over (α)}−φ_(T). In order tofacilitate comparisons with a threshold, put this difference in therange −180°<β_(T)≦180°, i.e., if β_(T)>180° then subtract 360°, but ifβ_(T)≦−180° then add 360°.

Step 5: Define a range of values for β_(T) that correspond to the userlying or sleeping on their back. In a preferred embodiment, classifyevery epoch for which −80°<β_(T)<80° as “on-back”. This range issymmetrical so the algorithm works for placement on either leg. Avoiding±90° by 10° excludes the values likely to be encountered when a userlies or sleeps on their side. In another preferred embodiment, thethresholds (which would reside at step 930 in FIG. 10) depend upon theleg on which the device is placed. For example, if the device is placedon the left leg, the most likely range of angles while lying on the backis 0°<β_(T)<80°. Alternatively, if the device is placed on the rightleg, the most likely range of angles while lying on the back is−80°<β_(T)<0°. Using asymmetric thresholds to accommodate the asymmetryof the normal range of motion of the leg relative to the torso mayimprove the accuracy of the static body rotational position detector.

Step 6: If the user with sleep apnea selects this option for TENS device100, then when the user is determined to be asleep, i.e., recumbent withlow activity, the TENS device notifies the user if they are on theirback for more than some set amount of time, e.g., a few minutes. Thisindication can be in the form of a vibration of the TENS device itself,or an alarm on their smartphone 860, for example.

Step 7: After determining the span(s) of minutes in which the user waslikely to be asleep, i.e., recumbent with low activity, determine thefraction of minutes in which the user was determined to be on theirback. Report this percentage to this user, e.g., with smartphone 860.

“Out-of-Bed” (OOB) Detector

In one preferred embodiment of the present invention, the 3-axisdirections of the accelerometer 152 are known and are fixed inrelationship to the lower leg when TENS device 100 is placed on theupper calf 140 of a user: the y-axis is aligned longitudinally along thelongitudinal axis of the lower leg of the user; the x-axis is disposedtangential to the surface of the lower leg of the user and perpendicularto the y-axis, and the z-axis points radially away from the surface ofthe lower leg of the user. Looking now at FIG. 7, where the Earth'sgravitational vector g is downward, the elevation angle θ (172)represents the angle between the positive accelerometer y-axis direction(174) and the true horizontal plane (170). Using the 50 Hz raw datacollected from accelerometer 152, which data contains the accelerationdue to gravity, processor 515 of user state detector 500 of TENS device100 can detect when the user is in an upright position, and analyzes thetemporal pattern of the acceleration data in order to identify steps(i.e., 610 in FIG. 11) associated with walking (see, for example, SusiM, Renaudin V, and Lachapelle G, Motion mode recognition and stepdetection algorithms for mobile phone users. Sensors,2013:13(2):139-1562). Processor 515 of user state detector 500 of TENSdevice 100 can also detect sequences of steps taken by a user in orderto determine when the user is walking (i.e., 620 in FIG. 11). Individualsteps taken by a user may be detected falsely by processor 515 of userstate detector 500 of TENS device 100 (e.g., due to other leg movement),however, the “walk detector” function of processor 515 is highlyspecific, inasmuch as the “walk detector” function of processor 515requires that the user's detected steps occur regularly and withspecific time intervals, in order for processor 515 to determine thatthe user is walking.

Using the orientation data stream, each one-minute epoch is classifiedas “upright” (i.e., 630 in FIG. 11) if data from accelerometer 152 isprocessed by processor 515 of user state detector 500 of TENS device 10and indicates that the absolute value of the mean elevation angle|θ|>45°. Contiguous sets of the “upright” epochs in which at least oneepoch includes walking or at least two epochs include stepping areclassified as “out-of-bed” (OOB) events 640, 641 (FIG. 11). This use ofstep and walk detectors makes the detection of “out-of-bed” (OOB) eventsmore specific and more accurate. By way of example but not limitation, auser can put their knees up in bed without falsely triggering an“out-of-bed” (OOB) event. In addition, epochs for which the meanelevation θ>75° (determined by processor 515 using data fromaccelerometer 152) are classified as “standing” (i.e., the user isstanding upright), and are also classified as “out-of-bed”(OOB) events641. Other values for these parameters are possible and are consideredto be within the scope of the present invention.

Sleep Detector

Intervals between “out-of-bed” (OOB) events are classified as“rest-in-bed” or “sleep segments” 650. It is understood that a user maynot be asleep in each of these “rest-in-bed” or “sleep segments” 650,and the term “sleep segment” implies only that the segments detected byaccelerometer 152 will be analyzed (i.e., by processor 515 of user statedetector 500 of TENS device 100) in order to determine whether the useris asleep. In the preferred embodiment, each sleep segment 650 ischaracterized by three basic features: mean activity A, mean elevationθ, and duration D. It should be appreciated that including a lessernumber of features (or a greater number of features) is considered tofall within the scope of the present invention. By way of example butnot limitation, other possible features include additional measures ofactivity within a segment (e.g., brief leg movement), measures ofchanges in leg elevation θ within a segment, and the duration of“out-of-bed” (OOB) events before and/or after a segment.

These features of a given sleep segment 650, which are determined byprocessor 515 using data from accelerometer 152 and/or gyroscope 163,are passed to a classifier 655 (FIG. 11) which determines whether thegiven segment meets requirements of sleep (e.g., “goodness-of-fit” ofthe segment feature parameters to their target ranges). It should beappreciated that the functions of classifier 655 may be implemented byappropriate software programming running on the aforementioned processor515 of user state detector 500 of TENS device 100, or the functions ofclassifier 655 may be implemented by another microprocessor of the sortwell known in the art with appropriate software programming forproviding the functions disclosed herein. In one form of the invention,each segment feature is compared against its own predeterminedthreshold. In another form of the invention, two or more segmentfeatures are evaluated together using a linear or nonlinear classifierfunction. In one preferred form of the invention, the classifierfunction is a naïve Bayesian classifier that evaluates all of thefeatures as they occur in a training set, and accounts for the priorprobability that the user is asleep given the actual time of daythroughout that particular segment; this classifier function thenreturns the probability that the user is asleep P(Sleep) and theprobability that the user is awake P(Wake). Based on theseprobabilities, each sleep segment 650 is characterized by K=log₁₀[P(Sleep)/P(Wake)]. Each sleep segment 650 is classified by classifier655 as “Asleep” if and only if K>K_(th). In the simplest embodimentcorresponding to the standard naïve Bayes classifier, K_(th)=0, in whichcase K>0 is equivalent to the condition P(Sleep)>P(Wake). In onepreferred form of the invention, K_(th)=0.5 to make the classifier morespecific for sleep (i.e., “Asleep”). Other classifiers and values forthese parameters are possible, and are considered to fall within thescope of the present invention.

The feature target range(s) and classifier threshold value(s) can beapplicable to all users, or tailored to selected group of users, orspecific to an individual user, or a combination thereof. For a givenuser, the feature target range(s) and classifier threshold values maystart out (i.e., be preprogrammed) as population default values. Thesepopulation default values can be updated based on specific indicationsby the user (e.g., “I am a light sleeper”). Finally, the values can befurther refined based on actual user sleep behavior previously measuredby TENS device 100 (e.g., a particular user's likely time of day forsleep calculation is modified by the user's prior history of sleep onsettime).

A sleep session 660 is a contiguous time interval during which the useris in bed for sleeping. In theory, a given sleep session 660 correspondsto the standard clinical definition of “time in bed”. In practice, agiven sleep session 660 it is detected as a series of sleep segments forwhich the starting and ending segments have K>K_(th). This definitionallows a given sleep session 660 to include some “out-of-bed” (OOB)events as may normally occur during the night, and two “out-of-bed”(OOB) events may be separated by a brief sleep segment, with K<K_(th).In addition, because users may watch television or read with theirleg(s) elevated, and users may be resting before bed (but not asleep),some sleep segments at the beginning of the night may have K>K_(th),however, the corresponding K values will typically be lower than thoseof sleep segments later in the night which are more clearly sleep. Inone preferred form of the invention, there are logical conditions whichneed to be met in order to start a sleep session 660 which excludesthose sleep segments corresponding to reading or watching television inbed; this can be accomplished by examining the history and trend of theK values recorded and analyzed by TENS device 100. By way of example butnot limitation, a given sleep session 660 starts with the first sleepsegment having a more stringent requirement of K>0.75, and ends when an“out-of-bed” (OOB) event is detected which lasts more than 15 minutes,with the additional condition that the last sleep segment included musthave K>K_(th). Other logical schemes and values for these parameters forthe first sleep segment, the last sleep segment and intermediate sleepsegments are possible and fall within the scope of the presentinvention.

Some users may have one (or more) long “out-of-bed” (OOB) event(s)during a given sleep session 660 (i.e., during the night while the useris sleeping) which results in TENS device 100 registering two or moresleep sessions 660. In one preferred form of the invention, there arelogical conditions which may be applied in order to merge the data formultiple sleep sessions 660. By way of example but not limitation, twosleep sessions 660 lasting at least 3 hours each and separated by an“out-of-bed” (OOB) event lasting less than 1 hour may be merged togetherto form one sleep session 660 in which the intervening “out-of-bed”(OOB)event is classified as “awake”. After the total (i.e., the merged) sleepsession 660 is defined, sleep metrics are computed by TENS device 100(e.g., by aforementioned processor 515 of user state detector 500 ofTENS device 100) and reported to the user.

Real-Time Estimation of Sleep Probability

In order to control the stimulation delivered by TENS device 100 to auser in real-time during a sleep session 660, the TENS device 100 usesthe information available for each minute (i.e., each epoch) to estimatethe probability that the user is sleeping, P(Sleep). In one embodiment,sleep probability (i.e., P(Sleep)) as a function of time depends on thesame three features used to assign a K value to a sleep segment asdescribed above (i.e., mean activity A, mean elevation θ, and durationD). Because P(Sleep) depends in part upon the duration of a particularsleep segment, P(Sleep) increases gradually following an “out-of-bed”(OOB) event. P(Sleep) increases with time more quickly if TENS device100 measures a lower mean activity level A and a mean elevation θ valuecloser to zero.

FIG. 12 shows P(Sleep) 670 for a given user as a function of timeduration 671 since the last recorded “out-of-bed” (OOB) event, in fourmodel cases: (i) mean activity A=0 and mean elevation θ=0°, (ii) meanactivity A=0 and mean elevation θ=45°, (iii) mean activity A=0.01 g andmean elevation θ=0°, and (iv) mean activity A=0.01 g and mean elevationθ=45°. The case 672 (A=0 and θ=0°) corresponds to ideal restful sleep.The extreme case 678 (A=0.01 g and θ=45°) corresponds to a user lying inbed with their knees up and very restless sleep. In the ideal case 672,P(Sleep)=0.5 at 24 minutes following the “out-of-bed” (OOB) event. Inthe extreme case, P(Sleep)<0.5 indefinitely. In the mixed cases 674 and676, P(Sleep)=0.5 at 73-89 minutes following an “out-of-bed” (OOB)event.

Real-Time Control of Stimulation Level

In one preferred form of the invention, a flag (i.e., a variable) called“AsleepForStim” is defined to indicate the real-time sleep state of theuser in order to control the stimulation intensity (e.g., a flag“AsleepForStim” is set by the software running on processor 515 of TENSdevice 100). Following an “out-of-bed” (OOB) event, for each minute(i.e., epoch), the TENS device 100 computes P(Sleep). When P(Sleep)>0.5,the AsleepForStim flag is set “true”. The AsleepForStim flag remains“true” until an “out-of-bed” (OOB) event is detected and has lasted forat least 15 minutes, then the AsleepForStim flag is set “false”.Consequently, the AsleepForStim flag will generally be “true” throughouta given sleep session 660, including any brief “out-of-bed” (OOB) eventsduring a given night (i.e., a given sleep session).

When stimulation is scheduled to start, TENS device 100 checks the valueof the AsleepForStim flag (i.e., to determine whether the flag is set to“true” or “false”). If the AsleepForStim flag is “false”, then thestimulation level will be unchanged. If AsleepForStim flag is “true”,the stimulation level will be reduced (unless the user chooses todisable this adaptive stimulation feature of TENS device 100).

Furthermore, if the AsleepForStim flag is “true” and the user enablesthe adaptive therapy onset mode (i.e., enables TENS device 100 todeliver adaptive stimulation depending upon user wake/sleep state),scheduled onset time for next therapy may be postponed based on areal-time measure of sleep quality called “sleep fragmentation”, as willhereinafter be discussed in further detail.

Real-Time Calculation of Sleep Fragmentation

Sleep fragmentation refers to brief arousals or awakenings that disruptthe normal sleep architecture, and often occurs often in peopleexperiencing chronic pain. The present invention provides the user withthe option to start therapy during sleep only when sleep is fragmented.This option balances the goals of using TENS device 100 to reduce painand improve sleep, while minimizing the possibility that the sensationof stimulation may itself disturb sleep.

In one preferred form of the invention, when stimulation is scheduled tostart, the TENS device 100 checks the value of the flag forAsleepForStim. If the flag for AsleepForStim is “true” and if TENSdevice 100 has been on the user's skin for at least an hour (i.e.,electrode array 120 of TENS device 100 has been in contact with theuser's skin for at least an hour), processor 515 of TENS device 100determines a value for a flag called “SleepFragmented” in the priorhour. If the SleepFragmented flag is determined to be “false”, i.e., ifsleep is very restful, then onset of stimulation is postponed. TENSdevice 100 then checks the flag for SleepFragmented status every 5minutes. When either the flag for AsleepForStim is “false” (i.e., theuser is awake), or the flag for SleepFragmented is “true” (i.e., sleepis no longer restful), stimulation by TENS device 100 is permitted tostart. In this way, stimulation is delivered by TENS device 100 only asneeded.

During a given sleep session 660, a user is considered to be awake ifthe user is either “out-of-bed” (OOB), or if the user's mean activity ina one-minute epoch A>0.01. A more sensitive measure of brief arousalsavailable from accelerometer data is leg movements (LM), computed usingthe 10 Hz activity stream, in which the effect of gravity has beenremoved. A leg movement (LM) is defined as an event in which theactivity detected by TENS device 100 exceeds a predetermined thresholdA2 and then falls below a predetermined threshold A1. In one preferredform of the invention, the predetermined thresholds are A1=0.02,A2=0.03, and there are no limits on its duration. In practice, activeepochs usually contain numerous events that meet this definition of legmovement (LM), so epochs with one or more leg movement (LM) eventsnormally include awake epochs as well as epochs with brief arousals. Ina preferred embodiment, the aforementioned Boolean flag calledSleepFragmented is “true” if and only if, in the last hour, the fractionof epochs with one or more leg movement (LM) is greater than 40%. Otherdefinitions of sleep fragmentation and values of these parameters arepossible and considered to fall within the scope of the presentinvention. In addition, these values may be set by TENS device 100, orthese values may be modified by the user.

FIG. 13 provides an illustrative example of the adaptive behavior of thetherapy onset based on user sleep state. Default therapy sessions areshown in trace 691. User “out-of-bed” (OOB) events are marked in trace692 (i.e., when the trace value is equal to 1). Sleep probability basedon user activity level, leg elevation, and “out-of-bed” (OOB) events isshown as trace 693. The AsleepForStim flag is shown as trace 694 (i.e.,the AsleepForStim flag is “true” when the trace value equals 1 and“false” when trace value equals 0). The SleepFragmented flag is shown astrace 695 (i.e., the SleepFragmented flag is “true” when the trace valueequals 1 and “false” when trace value equals 0). The OnsetDelay flag(which is the logic inverse of the SleepFragmented flag) is shown astrace 696 (i.e., the OnsetDelay flag is “true” when the trace valueequals 1 and “false” when trace value equals 0). Finally, adaptivetherapy sessions are shown as trace 697.

The sleep probability trace 693 is also shown in FIG. 13, withP(Sleep)>0.5 corresponding to “true” (i.e., “1”) for the first time at apoint near 132 minutes. The AsleepForStim flag trace 694 turns true(i.e., “1”) at 132 minutes, and remains true, even during the brief“out-of-bed” (OOB) event from 351-357 minutes (shown in trace 692). Anextended “out-of-bed” (OOB) event starts at 642 minutes, and theAsleepForStim flag becomes “false” at 662 minutes (shown in trace 694).

The onset of the scheduled therapy session 682 which would have occurredat the 240^(th) minute is delayed to the 360^(th) minute. Specifically,for each minute (i.e., epoch) when a therapy session was scheduled tostart (i.e., at the time instance when the value of trace 691transitions from 0 to 1), if the OnsetDelay flag (trace 696) is still“true”, the start of the therapy session is delayed. Since theOnsetDelay flag 696 becomes true at 171 minutes, and becomes false at359 minutes, the scheduled therapy session (trace 691) at the 240^(th)minute is delayed, and an actual therapy session 684 begins at the360^(th) minute.

Modifications of the Preferred Embodiments

It will be appreciated that the present invention provides atranscutaneous electrical nerve stimulator with automatic assessment ofsleep patterns and sleep characteristics based on monitoring of legactivities and leg orientations. Leg orientations include leg elevationand leg rotation state, and changes in leg elevation and leg rotationstates. The TENS stimulator may be pre-programmed to modify itsoperations in response to the detected user leg activities and legpositions during bed time. Individual aspects of the TENS stimulatoroperations (e.g., stimulation onset, stimulation pulse intensity, andstimulation session duration) are modified based on specific sleepcharacteristics. However, these operating parameters can be modifiedsimultaneously. In addition, leg orientation and leg activities are usedto assess sleep quality and sleep position, all are important aspects toimprove sleep and health. Leg activity patterns can also be used todiagnose sleep disorders such as periodic leg movement and the TENSstimulator can be used to alleviate excessive leg movement activitiesthat are disruptive to sleep.

While most sleep applications have a goal of prolonging good qualitysleep, it may also be desirable to regulate the duration of good qualitysleep each night. Another realization of the present invention is toprovide the user with feedback when the total duration of good sleep(i.e., non-fragmented sleep) reaches a target range. The feedbackprovided to the user can be in the form of mechanical vibrations from avibration motor (i.e., haptic feedback). The feedback can also be in theform of electrical stimulation (i.e., a stimulation pulse delivered byTENS device 100). In yet another realization of the present invention,feedback to the user is provided when a minimum time period of goodsleep is achieved and the sleep quality is transitioning fromnon-fragmented sleep to fragmented sleep.

The present invention can also be realized without the nerve stimulationfunctionality. Body movement and position can be monitored andquantified using the present invention without the need of nervestimulation. The monitoring apparatus (device) can also be placed inother body positions like upper arm of either limb.

Furthermore, many additional changes in the details, materials, stepsand arrangements of parts, which have been herein described andillustrated in order to explain the nature of the present invention, maybe made by those skilled in the art while still remaining within theprinciples and scopes of the invention.

What is claimed is:
 1. Apparatus for providing transcutaneous electricalnerve stimulation (TENS) therapy to a user, said apparatus comprising: ahousing; an application unit for providing mechanical coupling betweensaid housing and the user's body; a stimulation unit for electricallystimulating at least one nerve of the user; a sensing unit for (i)sensing the user's body movement and body orientation to determinewhether the user is in an “out-of-bed” state or a “rest-in-bed” state,and (ii) analyzing the sleep characteristics of the user during said“rest-in-bed” state; and a feedback unit for at least one of (i)providing the user with feedback in response to said analysis of saidsleep characteristics of the user, and (ii) modifying the electricalstimulation provided to the user by said stimulation unit in response tosaid analysis of said sleep characteristics of the user; wherein saidsleep characteristics comprise a likelihood measure of the user's sleepquality.
 2. Apparatus according to claim 1 wherein said application unitis a flexible band.
 3. Apparatus according to claim 1 wherein saidapplication unit determines whether said housing is mechanically coupledto the user's body.
 4. Apparatus according to claim 3 wherein amechanical element determines whether said housing is mechanicallycoupled to the user's body.
 5. Apparatus according to claim 4 whereinsaid mechanical element is a tension gauge.
 6. Apparatus according toclaim 3 wherein an electrical element determines whether said housing ismechanically coupled to the user's body.
 7. Apparatus according to claim1 wherein the user is determined to be in said “out-of-bed” state when abody orientation angle exceeds a threshold.
 8. Apparatus according toclaim 1 wherein the user is determined to be in said “out-of-bed” statewhen a body movement pattern matches a pattern for walking.
 9. Apparatusaccording to claim 1 wherein the user is determined to be in said“out-of-bed” state when a body orientation angle exceeds a threshold andwhen body movement pattern matches a pattern for stepping.
 10. Apparatusaccording to claim 1 wherein said sensing unit uses data from anelectromechanical sensor.
 11. Apparatus according to claim 10 whereinthe determination of whether said housing is mechanically coupled to theuser's body determines the usability of the data from saidelectromechanical sensor.
 12. Apparatus according to claim 10 whereinsaid electromechanical sensor is an accelerometer.
 13. Apparatusaccording to claim 10 wherein said electromechanical sensor is agyroscope.
 14. Apparatus according to claim 10 wherein saidelectromechanical sensor comprises both an accelerometer and agyroscope.
 15. Apparatus according to claim 10 wherein said sensing unitdetermines the user's body orientation angle with an analysis unitoperating on earth gravitational acceleration measurements from saidelectromechanical sensor.
 16. Apparatus according to claim 10 whereinsaid sensing unit determines a movement pattern of the user with ananalysis unit operating on said data from said electromechanical sensor.17. Apparatus according to claim 16 wherein said movement pattern isdetermined to be a walking pattern when a processed feature of said datais determined to be stepping continuously for a period of time. 18.Apparatus according to claim 17 wherein said processed feature isdetermined to be a stepping pattern when filtered components of the datafrom said electromechanical sensor match a target temporal pattern. 19.Apparatus according to claim 1 wherein said sleep characteristics forsaid time segment is determined based on at least one feature selectedfrom the group consisting of (i) mean leg activity, (ii) mean legelevation, (iii) leg rotation amount, and (iii) duration of the timesegment.
 20. Apparatus according to claim 19 wherein said determinationof said sleep characteristics is determined by a Bayesian classifieroperating on said at least one feature and a predetermined classifierthreshold.
 21. Apparatus according to claim 20 wherein saidpredetermined classifier threshold is a function of the time elapsedfrom the onset of said “rest-in-bed” state.
 22. Apparatus according toclaim 20 wherein said predetermined classifier threshold is a functionof the user's health profile.
 23. Apparatus according to claim 20wherein said predetermined classifier threshold is a function of theuser's past sleep characteristics.
 24. Apparatus according to claim 20wherein said sleep characteristics of said time segment is determined tobe “good” when the output of said Bayesian classifier exceeds saidpredetermined classifier threshold for said time segment.
 25. Apparatusaccording to claim 1 wherein said analysis of sleep characteristicsdetermines sleep quality for said time segment.
 26. Apparatus accordingto claim 24 wherein said sleep quality is determined to be fragmentedwhen the percentage of “good” sleep over said time segment is below apredetermined threshold.
 27. Apparatus according to 25 wherein said timesegment is at least one hour.
 28. Apparatus according to claim 24wherein said feedback unit calculates the accumulated time during whichthe user's sleep quality is classified as “good”.
 29. Apparatusaccording to claim 28 wherein said feedback unit is activated when thesaid accumulated time exceeds a predetermined threshold.
 30. Apparatusaccording to claim 1 wherein said feedback unit provides feedback to theuser via an alert delivered to the user through at least one selectedfrom the group consisting of a smartphone and another connected device.31. Apparatus according to claim 1 wherein said feedback unit providesfeedback to the user in the form of mechanical vibrations provided tothe user.
 32. Apparatus according to claim 1 wherein said feedback unitprovides feedback to the user in the form of electrical stimulationprovided to the user.
 33. Apparatus according to claim 26 wherein saidfeedback unit modifies said electrical stimulation provided to the userwhen said sleep quality is not fragmented.
 34. Apparatus according toclaim 33 wherein said electrical stimulation is modified to changestimulation intensity.
 35. Apparatus according to claim 33 wherein saidelectrical stimulation is modified to change stimulation frequency. 36.Apparatus according to claim 33 wherein said electrical stimulation ismodified to change the stimulation onset time.
 37. Apparatus accordingto claim 36 wherein said stimulation onset time change is to postpone ascheduled stimulation start time.
 38. A method for applyingtranscutaneous electrical nerve stimulation to a user, said methodcomprising the steps of: applying a stimulation unit and a sensing unitto the body of the user; using said stimulation unit to deliverelectrical stimulation to the user so as to stimulate one or more nervesof the user; analyzing electromechanical sensing data collected by saidsensing unit in order to (i) determine the user's body orientation, and(ii) quantify body activity levels so as to determine whether the useris in an “out-of-bed” state or a “rest-in-bed” state, whereby todetermine the quality and duration of the user's sleep during the“rest-in-bed” state; and modifying the electrical stimulation deliveredby said stimulation unit based on said sleep quality and said durationof the user's sleep during the “rest-in-bed” state.
 39. Apparatus formonitoring the sleep patterns of a user, said apparatus comprising: ahousing; an application unit for providing mechanical coupling betweensaid housing and the user's body; a sensing unit carried by the housingfor (i) sensing the user's body movement and body orientation todetermine whether the user is in an “out-of-bed”state or a “rest-in-bed”state, and (ii) analyzing the sleep characteristics of the user duringsaid “rest-in-bed” state; and a feedback unit for providing the userwith feedback in response to said analysis of said sleep characteristicsof the user.
 40. A method for monitoring the sleep patterns of a user,said method comprising of the steps of: applying a sensing unit and afeedback unit to the body of a user; using said sensing unit todetermine the user's body movement and body orientation to (i) determinewhether the user is in an “out-of-bed” state or a “rest-in-bed” state,and (ii) analyze the sleep characteristics of the user during said“rest-in-bed” state; and providing the user with feedback via saidfeedback unit in response to said analysis of said sleep characteristicsof the user.
 41. Apparatus for providing transcutaneous electrical nervestimulation (TENS) therapy to a user, said apparatus comprising: ahousing; an application unit for providing mechanical coupling betweensaid housing and the leg of a user; a stimulation unit for electricallystimulating at least one nerve of the user; and a sensing unit for (i)sensing the user's leg orientation and leg motion to determine whetherthe user is in an “out-of-bed” state or a “rest-in-bed state”, whereinsensing the user's leg orientation comprises determining the user's legelevation and leg rotation, and further wherein sensing the user's legmotion comprises determining the user's net activity and leg movements,and (ii) analyzing the sleep characteristics of the user during said“rest-in-bed” state; and a controller for modulating said stimulationunit based on said determinations made by said sensing unit.